2008 Cadillac STS Owner's Manual - Page 369

How to Check Lubricant To get an accurate reading, the vehicle should be on a level surface. If the level is below the bottom of the filler plug hole, located on the transfer case, you'll need to add some lubricant. Add enough lubricant to raise the level to the bottom of the filler plug hole. Use care not to overtighten the plug. What to Use Refer to the Maintenance Schedule to determine what kind of lubricant to use. See Recommended Fluids and Lubricants on page 6-13. Rear Axle When to Check Lubricant A. Drain Plug B. Fill Plug It is not necessary to regularly check rear axle fluid unless you suspect there is a leak or you hear an unusual noise. A fluid loss could indicate a problem. Have it inspected and repaired. 5-51